Size-dependent phase separation and thermomechanical properties of thermoplastic polyurethanes

Abstract

Over the years, the manipulation of polymer microphase separation associated with molecular architectures has been holding great promise for rendering structure-property relationship. A series of poly (urea/malonamide) dendrons bearing rigid adamantanes in the periphery were developed to serve as branching hard segments (HS) for thermoplastic polyurethanes (TPUs) either in end-capping or pendant manner. Thermal properties, crystalline structures, and mechanical properties of the TPUs were investigated by DSC, X-ray scattering, and DMA, respectively. The introduction of the branching units with bulky adamantanes would expectedly hinder the crystallization of HS. Intriguingly, the dendrons not only accelerate the crystallization of the soft segment (SS, based on polycaprolactone polyol (PCL)), but promote the phase separation between HS and SS to form distinct microdomains as well. These enhanced effects revealed a size-dependent relationship with growing size (or generation) of the branching HS. With the high SS crystallinity that can freeze the chain mobility and the robust HS domains that work as the physical crosslinking points, the resulting TPUs incorporated with adamantane-bearing units show superior shape memory behaviors. This work demonstrates that the molecular engineering on the architectures can significantly tailor the microstructures and properties of thermal plastic polymers.